This time Blizzard wasn't so lazy and properly updated the TOC on the PTRs to 40200 which is less of a hassle
I'm interested in the solutions for forwards compatibility, and I want to share some myself

It saves a reference to the old handler for CLEU and then declares a new one. The new one then has the new parameters in the function-call (so things line up correctly) and then just passes the all parameters besides the new ones to the old handler.

It only uses tailcalls if the version is NOT 4.1, so for standard users suffer no performance penalties. Omegal's solution is essentially the same thing, just that he created a second function to call the original, and I instead made the function call itself.

Note the unorthodox way of calculating the TOC only because for most of the 4.1 PTR testing, the 4th return of GetBuildInfo() returned 40000 rather than 40100.